This cover for the novel provides an artist's conception of the hypnobioscope:

The first use of this idea outside science fiction was apparently the invention of the "Psycho-Phone" by In 1927 by Alois Benjamin Saliger . He asserted that "It has been proven that natural sleep is identical with hypnotic sleep and that during natural sleep the unconscious mind is most receptive to suggestions." Modern research indicates that "sleep teaching" doesn't really work.

Unlike the devices used to present information to the brain by the roundabout method of playing it out loud and then entering through the ears, the hypnobioscope acts directly on the brain itself.

Compare to hypnopaedia from Aldous Huxley's 1932 novel Brave New World and the toposcope from Cities in Flight (1955) by James Blish.